Now, we know why. The reality TV star, who shocked the fans of the show by losing 155 pounds, said that she follows a strict "super healthy" diet and exercise regimen laid out for her by the show's dietician, Cheryl Forberg.

"First and foremost, my goals are to be healthy and strong," the 24-year-old, who is now a size 0/2, told reporters, according to People magazine. "I'm an athlete. I've been an athlete since I was a little girl. And I went on 'The Biggest Loser' journey to find that confidence that I lost."

For breakfast, Frederickson, who has discovered "a zest for looking up recipes and trying them," sticks to egg white French toast or an omelet made with egg whites, spinach, tomatoes and mushrooms.

Meanwhile, before the weigh-in, she said she'd been taking "maybe three, four [exercise] classes a day," including Zumba and spin. "I even went home over the holidays to Minnesota and I went running outside," she added.

Now that the show has ended, Frederickson said she's in "maintenance mode."

"[I'm looking forward to] this next part of my journey," she said, "as my body balances and, you know, finds its rhythm."